In addition to killing the two children, police say Avery also stabbed her 5-year-old daughter, Taniya Harris, and her 8-year-old son, Martello Harris.

Those two children were taken to a local hospital in critical condition, said Montgomery County Police Capt. James Daly.

Investigators learned the two women believed that they were performing an exorcism, according to a release from police.

Daly said police learned of the incident at about 9:30 a.m. Friday after one of Avery’s neighbors spotted a car in the townhome parking lot with its door ajar and stained with blood.

Police said the person who first reported the incident also told them a knife was lying on the ground next to the vehicle.

When police arrived, they found the keys still in the car and let themselves into the home, a yellow townhome in the Seneca Forest community.

Inside Avery’s home, police discovered Norell and Zyana’s bodies, which had been stabbed multiple times, and their older siblings, who were in critical condition. They are still in the hospital, according to police.

Jennifer Cate, Avery’s neighbor, was lying in bed when she heard police arrive at the home Friday morning.

“I saw the police officers go in, and then I saw the police officers running back out. ... One person was tackled,” she said.

Police arrested Avery and initially hospitalized Monifa Denise Sanford, 21, with “superficial” wounds. They have since arrested and charged her with along with Avery. Sanford lived at the home with Avery and the children, police said.

Police are still trying to piece together the details of what happened, but say the incident might have started Thursday night.

Around 10 p.m. Thursday, a neighbor called police and told them a young child was sitting alone in a car the the community parking lot.

While that neighbor was on the phone with police, two women confronted the person and took the child inside the home.

When police went to the home Thursday night, no one answered the door, Daly said.

Police alerted Child Protective Services on Thursday night and Daly said the department was asked to check on the welfare of the children at the home Friday morning.

Neighbors who lived nearby said little about Avery and her children. One person said the family had moved to the community in the past year.

On Monday, the yard in front of the house was festooned with teddy bears and flowers left by mourners.

Montgomery County Police Chief Tom Manger called the slayings “heartbreaking.”

“Our thoughts are with the family and friends of the victims along with the 911 operators, police officers, evidence technicians, and fire and EMS personnel that responded,” he said.

John McCarthy, the county’s State’s Attorney, was outside the home Friday, and said he would be prosecuting the case himself.